Many approaches are used to whiten teeth. Two of the most common approaches use abrasives or chemical whiteners, such as peroxides. Abrasives in combination with a polishing action are used to polish discolorations and stains off of the surface of the teeth. Thus, light reflected from the teeth represents the true intrinsic color of the teeth. Abrasives are a major element of most consumer toothpastes and prophyaxis pastes used by dentists. Because abrasives only work on the surface of the teeth, the intrinsic color of the tooth is largely unchanged. As such, abrasives only offer limited effectiveness in whitening of the teeth.
The second approach is the use of chemical whitening actives in a composition to intrinsically and extrinsically whiten teeth. Chemical whitening actives are applied to the teeth for period of time to allow the active to act upon the tooth and provide an improvement in the whiteness of the teeth. Whiteners are commonly applied to the teeth using toothpastes, rinses, gums, floss, tablets, strips and trays. A common chemical whitening active is peroxide. Often, strips and trays are used to apply peroxide for contact times beyond that achievable with typical toothbrushing. Concentration of the whitening active, contact time and number of applications are some of the primary parameters which dictate the rate and amount of whitening achieved with peroxide based tooth whitening compositions. Whitening products using a strip of material in combination with a chemical whitening active are known in the art. For example, U.S. Pat. Nos. 5,891,453 and 5,879,691, the substances of which are incorporated herein by reference, describe a whitening product comprising a flexible strip of material and a whitening composition. The whitening composition can include a peroxide active.
It is commercially desirable to increase the whitening efficacy of products in order to deliver a more satisfying product experience. Increasing the concentration of peroxide, holding all other parameters essentially constant, generally results in faster whitening per time of use. Similarly, longer contact times produce more whitening provided the peroxide is maintained on the tooth surface. Thus, increasing concentration, increasing wear time and increasing number of applications can be effective methods of achieving higher degrees of tooth whitening from a tooth whitening product. Each of these parameters also may have a negative impact on the consumer's experience. Increasing the concentration of the peroxide in the whitening composition, holding all other parameters essentially constant, can produce more tooth sensitivity and cause more soft tissue irritation. Sufficiently high concentrations of peroxide may require a physical barrier, such as a rubber dam, to prevent the peroxide from contacting and burning the soft tissue thereby making the use of the high peroxide concentrations inconvenient and impractical for unsupervised at home and repeated use. In fact, even conventional chairside tooth whitening compositions having a peroxide concentration equivalent to 13% hydrogen peroxide often utilize a rubber dam to protect the soft tissue during the bleaching process. Increasing the use time will increase the amount of tooth sensitivity and gingival irritation as well as make the product more inconvenient to use. Similarly, increasing the number of uses also makes the product less convenient to use.
Thus, there is a desire to provide whitening products that achieve the increased whitening efficacy associated with increased peroxide concentrations while avoiding attendant soft tissue irritation so often associated with these higher peroxide levels. Still further, there is a desire to provide convenient tooth whitening products that utilize higher peroxide concentrations without the need for artificial barriers, such as rubber dams or other ginigival protectants.